1. Technical Field
The present invention relates to systems, devices and methods for performing a medical procedure, wherein the system, apparatus and method includes the measurement of at least one parameter related to the microwave energy delivered to the handpiece of the microwave energy delivery device.
2. Description of Related Art
During microwave ablation procedures, the electrical performance of the microwave energy delivery system (e.g., the system including a generator, a microwave energy delivery device, a waveguide configured to delivery the microwave energy signal from the generator to the handpiece of the device, and an antenna) changes throughout the course of an ablation treatment. The change in performance may be due to a change in the delivery device, a change in the tissue properties or a change in the delivery path. The ability to observe parameters indicative of these changes provides better control of the delivery of the microwave energy.
For example, measuring antenna impedance is a common method for determining antenna performance and/or a change in an antenna property. Microwave systems are typically designed to a characteristic impedance, such as, for example, 50 Ohms, wherein the impedance of the generator, the delivery system, the ablation device and tissue are about equal to the characteristic impedance. Efficiency of energy delivery decreases when the impedance of any portion of the system changes.
With low frequency RF systems impedance can easily be determined by measuring the delivered current at a known voltage and calculating tissue impedance using well known algorithms. Obtaining accurate measurements of tissue impedance at microwave frequencies is more difficult because circuits behave differently at microwave frequency. For example, unlike an electrode in an RF system, an antenna in a microwave system does not conduct current to tissue. In addition, other components in a microwave system may transmit or radiate energy, like an antenna, or components may reflect energy back into the generator. As such, it is difficult to determine what percentage of the energy generated by the microwave generator is actually delivered to tissue, and conventional algorithms for tissue impedance are typically inaccurate.
Therefore, other methods of measuring impedance are typically used in a microwave system. One well known method is an indirect method using measurements of forward and reverse power. While this is a generally accepted method, this method can also prove to be inaccurate because the method fails to account for component losses and depends on indirect measurements, such as, for example forward and reverse power measurements from directional couplers, to calculate impedance. In addition, this method does not provide information related to phase, a component vital to determining antenna impedance.
The present disclosure describes a microwave energy delivery system that includes a microwave energy delivery device configured to measure at least one parameter related to the energy delivered to the handpiece of the microwave energy delivery device.